In many sensor applications, such as for magnetic field, temperature or mechanical strain sensing, resistive sensing elements are used, which are influenced by the physical quantity to be measured. To produce a reliable and a sensitive output signal, the sensing elements may be connected in a bridge configuration such as a Wheatstone bridge. This provides a balanced differential output voltage between two nodes of the bridge, the differential output voltage being proportional to a change in the physical quantity being measured and to a supply voltage across the bridge. This analogue differential signal may be digitised by connecting the output voltage to the inputs of a differential Analogue to Digital Converter (ADC).
The performance of the ADC is to a large extent determined by the accuracy of two reference voltage levels, each of which may be provided by a reference voltage source. The two reference voltage levels may be provided indirectly from the supply voltage by means of an appropriate circuitry, for example using voltage dividers. A drawback of this is that it may be difficult to generate low noise and accurate reference voltage levels. Further, a significant fraction of the power consumed will tend to be used for the generation of the reference voltage levels. With high frequency noise present at the supply voltage the frequency bandwidth of the reference voltage levels will be different than the frequency bandwidth of the bridge signals. This means that high frequency noise present on the supply voltage will not be suppressed due to a phase and/or amplitude difference between signal and reference, but instead converted into the digital domain. This could even result in an unwanted aliasing. High frequency noise can further fold back into the Band of Interest (BOI) of the ADC. In particular in case of comparatively intense noise being present on the supply voltage, a large full signal swing of the differential output voltage must be processed by the ADC, resulting in high linearity requirements of the ADC.
As a consequence of the drawbacks mentioned above, the performance of existing sensor systems comprising sensing elements arranged in a full bridge configuration and an ADC for providing a digital output may be reduced.